A passenger vehicle is typically provided with a spare tire pan in a rear part of the vehicle body. As the current vehicle body typically has a monocoque structure combining a number of sheet steel pieces having relatively small thicknesses, it is a challenge to achieve a required mechanical strength and rigidity against a rear end crash while forming a space for receiving a spare tire.
The rigidity and mechanical strength of a vehicle body can be increased by increasing the thickness of the sheet steel, but it has the disadvantage of increasing the manufacturing cost, impairing the fuel economy and lowering the dynamic performance of the vehicle. Therefore, there have been various proposals to increase the mechanical strength of a rear part of a vehicle without increasing the thickness of the sheet steel that is used.
In the vehicle body structure disclosed in Japanese patent No. 3620288, a cross member for supporting a wheel suspension system is provided immediately ahead of a spare tire pan formed by downwardly recessing a rear floor panel between a pair of rear side frames. The spare tire is received in the spare tire pan in a horizontal orientation. Another cross member for supporting a seat catcher for engaging a rear seat is provided ahead of this cross member. These two cross members jointly form a region which is highly resistant to deformation while the spare tire pan is formed as a more readily deformable part so that the spare tire may tilt downward around the front end thereof at the time of a rear end crash. Thereby, the impact energy of the rear end crash can be favorably absorbed in a stable manner.
In the rear vehicle body structure disclosed in Japanese patent laid open publication (kokai) No. 2004-314673, a spare tire pan is slanted with the forward end down, and a front vertical wall of the spare tire pan is connected to a horizontal front floor panel. A slanted upright wall member is connected between the front floor panel and front vertical wall so as to form a closed cross section along the junction between front floor panel and front vertical wall. Thereby, the reinforced front vertical wall of the spare tire pan is given with an increased rigidity so as to protect a fuel tank located ahead of the front vertical wall against the impact of a rear end collision without unduly reducing the space available for the fuel tank.
In the example disclosed in Japanese patent laid open publication (kokai) No. 2006-193046, a spare tire is received horizontally in a spare tire pan defined by recessing a part of a rear floor panel, and the spare tire pan is reinforced by a longitudinal member attached to the lower surface of the rear floor panel. The rear end of the longitudinal member is spaced from a vertical wall of a rear end panel. According to this arrangement, when an impact is received from the rear, the spare tire is prevented from being dislodged, and caused to be tilted so as to effectively absorb the impact.
These prior inventions have various shortcomings. If the rear vehicle body structure is configured to drop the rear end of a spare tire at the time of a rear end collision as proposed in Japanese patent No. 3620288, the deformation of the spare tire pan cannot be effectively utilized for the absorption of the impact energy of a rear end collision, and this limits the capability of the rear vehicle body to effectively absorb the impact energy at the time of a rear end collision particularly when hit by a tall vehicle having a front bumper at a relatively high position.
According to the invention disclosed in Japanese patent laid open publication (kokai) No. 2004-314673, the rear end of the spare tire pan is raised without fail upon receiving the impact of a rear end collision. However, because the front vertical wall of the spare tire pan hangs over the front part of the spare tire, the spare tire is caught by this overhang as the rear end thereof is raised due to the impact of a rear end collision, and the rear end of the spare tire can be raised only to a limited extent. Therefore, the deformation stroke of the rear vehicle body is limited by such a behavior of the spare tire at the time of a rear end collision. Also, because of the absence of a cross member that connects the rear frames with each other, the impact of an offset rear end collision is not favorably distributed to the rear vehicle body.
According to the invention disclosed in Japanese patent laid open publication (kokai) No. 2006-193046, the spare tire is disposed horizontally and is fixedly secured to the floor panel, and the spare tire may be raised at the time of a rear end collision but only to a limited extent because a reinforcement member resists the rising movement of the spare tire. As a result, the deformation stroke at the time of a rear end collision is limited. Because of the absence of a cross member that connects rear parts of rear frames, the impact of an offset rear end collision is not favorably distributed to the rear vehicle body. These problems are particularly acute in the case of a hatchback passenger vehicle which does not have a bulkhead separating a passenger compartment from a luggage compartment, and has rear seats located relatively close to the rear end of the vehicle body.
These problems may be alleviated by increasing the mechanical strength of the rear side frames, but the rear side frames are capable of supporting loading that is applied to a limited region of the vehicle body, and may not be adequately able to support the load of a rear end collision depending on the way the rear end collision occurs.